NATURAL SCIENCES OP PHILADELPHIA. 313 



from the beaks at an angle of about 100, the posterior slope being distinctly 

 concave. Beaks prominent, incurved, and located half way between the mid- 

 dle and the anterior end ; lunule deeply excavated, but not defined by a distinct 

 marginal angle ; escutcheon lanceolate, rather deep and circumscribed by a mar- 

 ginal ridge ; surface marked by fine lines of growth, with sometimes near the 

 free borders a few concentric wrinkles. Length 1'30 inches; height 0*85 

 inch ; convexity (of a right valve) 0*39 inch. 



Locality and position. Brackish-water deposits, Bear River, lat. 40 k 12' 

 north, long. 110 52' west. 



Coebula (Potamomya ?) concenteica, Meek. Shell ovate subtrigonal, gibbous 

 in the umbonal region, narrow and compressed, or subrostrate behind, not very 

 distinctly inequivale ; anterior side obliquely subtruncate above, and narrowly 

 rounded below ; ventral border semiovate in outline, being more prominent in 

 the central and anterior regions than posteriorly ; anal extremity very narrowly 

 rounded or subangular ; beaks elevated, incurved, and placed in advance of 

 the middle ; lunule oval and rather deep, though not distinctly circumscribed, 

 escutcheon narrow, impressed and well defined ; surface ornamented by fine lines 

 of growth, and small regular, equidistant concentric wrinkles ; (hinge and in- 

 terior unknown). Length about 1*40 inches; height 0*90 inch; convex- 

 ity about 0"65 inch. 



Locality and position, same as last. 



Coebula (Potamomya?) Engelmanni, Meek. Shell rather small, transversely 

 subovate, gibbous in the umbonal region ; anterior side rather narrowly rounded; 

 base semiovate, being more prominent towards the front than behind ; poste- 

 rior side narrow, and truncate at the immediate extremity, having a mode- 

 rately distinct angle extending from the back part of the beaks obliquely 

 backwards to the lower part of the slightly truncate posterior end, beaks de- 

 pressed, located in advance of the middle ; surface ornamented by small very 

 regular concentric wrinkles. (Hinge and interior unknown.) Length (of a 

 right valve) 0-39 inch ; height 0.21 inch ; convexity, 0*11 inch. 



Locality and position, same as last. 



GASTEROPODA. 



Melania humeeosa, Meek. Shell rather thick, sub-ovate ; spire conical, 

 not very much elevated ; volutions about five and a half, distinctly shouldered ; 

 and more or less angular, last one comparatively large, rounded and con- 

 tracted below ; suture distinct ; surface ornamented by about fourteen rather 

 strong, regular vertical folds or costae to each turn ; folds obsolete on the 

 lower part of the body whorl, but becoming more strongly defined at the 

 shoulder, where they often terminate in spine- like nodes, so as to give the 

 whorls a distinctly coronate character ; crossing the3e folds or costae, there are 

 on each volution of the spire about four, and on the last whorl some seven or 

 eight, regular, equidistant revolving lines, or small ridges. 



Locality and position, same as foregoing. 



Melania Simpsoni, Meek. Shell elongate conical ; spire attenuate and 

 pointed ; volutions about ten, flattened or more or less convex, increasing 

 gradually in size, last one rounded below, suture sometimes linear, in other 

 instances more strongly defined in consequence of the greater convexity of the 

 whorls ; surface marked by fine lines of growth, and small slightly arched 

 vertical folds, which vary in size and regularity on different specimens, and 

 are crossed by small obscure thread-like revolving lines ; aperture ovate ; 

 columella moderately sinuous below ; lip somewhat retreating above, and 

 prominent below the middle. Length 0-78 inch ; breadth 0-30 inch; apical 

 angle nearly or quite regular, divergence about 26. 



The specific name is given in honor of Capt. J. H. Simpson, Top. Engr's. U. 

 S. Army, commander of the Utah Exploring Expeditions, &c. 



I860.] 



